void al_color_rgb_to_cmyk(float red, float green, float blue,
   float *cyan, float *magenta, float *yellow, float *key)
Introduced in 5.0.0

Each RGB color can be represented in CMYK with a K component of 0 with the following formula:

C = 1 - R
M = 1 - G
Y = 1 - B
K = 0

This function will instead find the representation with the maximal value for K and minimal color components.

See also: al_color_cmyk, al_color_cmyk_to_rgb

Examples: ex_color